1. Field of the Invention
The present invention relates to nonreciprocal circuit devices such as isolators and circulators used in microwave bands and the like, methods for manufacturing the nonreciprocal circuit devices, and communication apparatuses incorporating the nonreciprocal circuit devices.
2. Description of the Related Art
Referring to FIG. 12 and FIGS. 13A to 13C, a description will be given to a method of marking a nonreciprocal circuit device according to the related art.
FIG. 12 is a flowchart showing the process of manufacturing the nonreciprocal circuit device. FIG. 13A shows a conceptual view of stamping, FIG. 13B shows the front view of a printing die, and FIG. 13C shows an enlarged view of a character printed with the printing die.
As shown in FIG. 12, in the fifth step of the process, the characteristics of the nonreciprocal circuit device are measured and in the sixth step, information including a product number and a lot number is printed on the nonreciprocal circuit device and sent to a step of conducting delivery inspection. The step of printing is performed by stamping, transfer printing, screen printing, ink-jet printing, or the like.
Here, printing by stamping will be described with reference to FIG. 13A.
After its characteristics have been determined, the nonreciprocal circuit device is placed in a predetermined position. Then, the product number, the lot number, and the like are printed in a predetermined position on the nonreciprocal circuit device by a printing die on which ink is applied in advance. The ink of printed characters is dried and hardened by heating. The completed product is then sent to the next step to perform delivery inspection.
However, in the nonreciprocal circuit device of the related art, there are several problems.
When ink is applied to the printing die, the viscosity of the ink changes with time and temperature in work environment. Thus, variations in printing occur even under the same printing condition. Additionally, when stamping is repeated for a long time, the printing die is worn out, also causing variations in printing.
Similarly, in transfer printing and screen printing, variations in printed characters are caused due to influence of the viscosity of ink and the abrasion of the screen. Also, these printing methods require an original form in advance. As the number of different types of products increases, the number of original forms also increases. As a result, more storage space is necessary for storing the original forms and the storage of the original forms becomes complicated.
In addition, when printing is performed by pressing, when compared with non-contact printing methods, the original forms of a printing die, a transfer plate, or the like are significantly worn out and thereby the life of the original forms is shortened. Consequently, the cost of auxiliary materials increases.
Additionally, due to the use of ink, the work environment becomes soiled, which leaves stains on the nonreciprocal circuit device.
When using a rubber plate as an original form, it is possible to form a character having a maximum line width of approximately 50 xcexcm on the plate. However, since the rubber plate needs to be pressed against a printing surface of the device during the printing process, the printed character is crushed flat. Thus, the line width of the character becomes approximately 100 xcexcm at minimum.
In this case, as shown in FIG. 13C, the printed character has a size of at least approximately 0.6xc3x970.4 mm. Thus, characters smaller than that cannot be printed. Consequently, when the nonreciprocal circuit device is miniaturized, it is impossible to print the same information as that printed in the large size device and the number of characters needs to be reduced.
On the other hand, when the number of characters is reduced, the product information is also reduced and therefore the following problems occur.
When the number of lot characters is reduced, the number of products per lot increases. Then, in the following step or when defaults occur after the product is incorporated in a communication apparatus, workloads such as screening increases. When the number of product-name characters is reduced, failure in identifying the kinds of products frequently occurs. For example, other kinds of products may be mixed in mistakenly. This is particularly problematic with nonreciprocal circuit devices, since there are various kinds of products having the same configuration but using different frequency bands. Thus, without marked characters it is often difficult to identify the product by its appearance, such as its outer configuration.
In the ink-jet printing method, since there is no need for an original form and it is a non-contact method, production cost can be reduced. However, stains are often left due to splattered ink and the like.
In addition, since the ink-jet nozzle constantly becomes dirty, frequent cleaning-up and maintenance is needed.
Furthermore, even in the ink-jet printing method, since printing is performed by spattering ink, there is a problem about the resolution of printed characters. Thus, when a nonreciprocal circuit device is miniaturized, the ink-jet method has a limitation to the dimensions of characters as in the case of the stamping method.
Accordingly, one object of the present invention to provide a method of manufacturing a highly reliable nonreciprocal circuit device at low cost. In this method, even when the nonreciprocal circuit device is miniaturized, marking can be clearly performed thereon without reducing the amount of product (or other) information. It is another object of the invention to provide a nonreciprocal circuit device manufactured by the method of the invention. Furthermore, it is another object of the invention to provide a communication apparatus incorporating the nonreciprocal circuit device.
According to a first aspect of the present invention, there is provided a method of manufacturing a nonreciprocal circuit device including a metal case containing central conductors, a ferrite core arranged near the central conductors, and a permanent magnet for applying a static magnetic field to the ferrite core. The method includes a step of marking onto the metal case of the nonreciprocal circuit device by irradiating with a laser beam.
In addition, the method may further include a step of heating the entire nonreciprocal circuit device after the laser marking.
In addition, the method may further include a magnetic-force-adjusting step for magnetizing or demagnetizing a permanent magnet prior to the heating step.
In addition, in the heating step, both of the thermal demagnetization of the permanent magnet and the removal of stains generated due to the marking may be performed.
In addition, in this method, the heating temperature in the heating step may be set between 110xc2x0 and 210xc2x0 C.
In addition, the method may further include a step of applying solder paste to portions where the components comprising the nonreciprocal circuit device are bonded with each other, prior to the heating step.
In addition, when the method includes the above solder-applying step, the heating temperature in the heating step may be set between 210xc2x0 and 310xc2x0 C.
In addition, the metal case may include an upper yoke and a lower yoke and the laser marking may be performed onto the upper yoke before the upper and lower yokes are bonded with each other.
In addition, in the method, the laser marking may be performed by continuously irradiating with a laser beam.
In addition, in the method, the laser marking may be performed by irradiating with a pulsed laser beam.
In addition, the laser beam may have a wavelength of 10 xcexcm or less.
Furthermore, the used laser beam may be a YAG laser or a YVO4 laser.
According to a second aspect of the present invention, there is provided a nonreciprocal circuit device including central conductors, a ferrite core arranged near the central conductors, a permanent magnet for applying a static magnetic field to the ferrite core, and a metal case containing the central conductors, the ferrite core, and the permanent magnet. In the nonreciprocal circuit device, a coating layer including a silver layer is formed on a surface of the metal case or on surfaces of the upper and lower yokes to perform marking onto the coating layer by irradiating with a laser beam.
This nonreciprocal circuit device may further include a layer formed of nickel or copper arranged under the silver layer.
In addition, in the nonreciprocal circuit device of the invention, the entire thickness of the coating layer may be 3 xcexcm or more.
Furthermore, the nonreciprocal circuit device may further include a nickel layer formed on the silver layer.
According to a third aspect of the invention, there is provided a communication apparatus including the nonreciprocal circuit device according to the invention.